1. Field of the Invention
The present invention relates to a fixing device of an image forming apparatus such as a copier, a printer, or a facsimile which is loaded therein for heating and fixing a toner image and a fixing method for the image forming apparatus.
2. Description of the Background
As a fixing device used for an image forming apparatus such as an electro-photographic copier or a printer, there is a fixing device available for inserting a sheet of paper through a nip formed between a pair of rollers composed of a heat roller and a pressure roller or similar belts and heating, pressurizing, and fixing a toner image. In such a heating type fixing device, to keep the heat roller at a constant fixable temperature, the surface temperature of the heat roller is detected by a temperature sensor and a heating source is controlled so as to be turned on or off according to detection results.
As a temperature sensor, in recent years, as an infrared temperature sensor, a non-contact temperature sensor for detecting temperature without making contact with non-heated members of the heat roller and fixing belt is used. A non-contact infrared temperature sensor using a thermopile does not damage the surfaces of the heated members and can lengthen the life span of the heat roller.
However, when such a non-contact infrared temperature sensor is used, not only infrared rays emitted from the surfaces of the heated members but also infrared rays radiated from other than the surfaces of the heated members enter the conventional infrared temperature sensor by irregular reflection. Therefore, there is a risk that the infrared temperature sensor may detect the temperatures of the heated members as temperatures different from the actual temperatures.
Therefore, in a fixing device for detecting the surface temperatures of the heated members by the non-contact infrared temperature sensor, development of a fixing device of an image forming apparatus for preventing an incorrect detection of temperature caused by irregular reflection and incidence of infrared rays other than the infrared rays radiated from the heated members, thereby detecting the temperatures of the heated members with high precision, controlling exactly the temperatures of the heated members, improving the fixing property of the heated members, and obtaining a high image quality is desired.